fix: better error message for get_config close #13889 (#15943)

Signed-off-by: yihong0618 <zouzou0208@gmail.com>

vllm/transformers_utils/config.py

@@ -262,6 +262,11 @@ def get_config(
                                      MISTRAL_CONFIG_NAME,
                                      revision=revision):
                 config_format = ConfigFormat.MISTRAL
+            else:
+                raise ValueError(
+                    "Could not detect config format for no config file found. "
+                    "Ensure your model has either config.json (HF format) "
+                    "or params.json (Mistral format).")
 
         except Exception as e:
             error_message = (
@@ -324,7 +329,14 @@ def get_config(
     elif config_format == ConfigFormat.MISTRAL:
         config = load_params_config(model, revision, token=HF_TOKEN, **kwargs)
     else:
-        raise ValueError(f"Unsupported config format: {config_format}")
+        supported_formats = [
+            fmt.value for fmt in ConfigFormat if fmt != ConfigFormat.AUTO
+        ]
+        raise ValueError(
+            f"Unsupported config format: {config_format}. "
+            f"Supported formats are: {', '.join(supported_formats)}. "
+            f"Ensure your model uses one of these configuration formats "
+            f"or specify the correct format explicitly.")
 
     # Special architecture mapping check for GGUF models
     if is_gguf: